1. Field of the Invention
The present invention relates to a sewing machine provided with mechanisms for driving vertical and front-to-rear movement of a feed dog.
2. Description of the Related Art
There has been known a conventional electrically-controlled household sewing machine that stores pattern data for a plurality of embroidery patterns. The pattern data can be stored either in a ROM (non-volatile memory) of the sewing machine's control device, or in a ROM card, which is an external memory medium. Embroidery patterns corresponding to the pattern data are displayed on a display of the sewing machine. The user can switch through display of different patterns to select a desired pattern. With this configuration, users can select not only practical patterns, such as straight line stitches or zigzag stitches, but also embroidery patterns. The sewing machine then sews a pattern based on the sewing data corresponding to the selected pattern.
A sewing machine forms stitches in the following manner. First, the sewing needle is driven to move downwards, thereby drawing upper thread from an upper thread spool. When the needle is driven to move upwards, the upper thread forms a loop at the eye of the needle. The loop taker beak of a horizontally disposed loop taker or other loop taker catches the loop of the upper thread loop that extends through the eye of the sewing needle. The loop taker then passes the lower thread through the loop. Then, a thread take up lever is driven to move upward, to tighten the upper thread loop around the lower thread.
The sewing machine includes a feed dog for transporting the workpiece cloth when a practical pattern is to be sewn. In this case, after the workpiece cloth is placed on the needle plate of the bed portion of the sewing machine, the feed dog first protrudes through a slot in the needle plate, that is, above the upper surface of the needle plate, and then moves backward, thereby drawing the workpiece cloth backwards. Then, the feed dog drops below the upper surface of the needle plate and moves forward. Once the feed dog has moved forward, it again protrudes above the upper surface of the needle plate and moves backward. The workpiece cloth is transported by these four movements of the feed dog.
On the other hand, when an embroidery pattern is to be sewn, the workpiece cloth is mounted in a sewing pattern frame which is mounted on the bed portion. The embroidery frame is driven to move forward, rearward, leftward, and rightward to move the workpiece cloth to a desired position with respect to the sewing needle. Because the feed dog is not needed during embroidery sewing, a feed dog retracting mechanism is provided for retracting the feed dog below the needle plate. The feed dog retracting mechanism maintains the feed dog in this retraction position during embroidery sewing. This also prevents the feed dog from interfering with movement of the workpiece cloth supported in the embroidery frame.
Japanese Patent-Application Publication No. SHO-63-64992 discloses a sewing machine capable of sewing embroidery patterns. A feed dog lowering device is provided for retracting the feed dog below the level of the needle plate by driving a solenoid to disrupt transmission of drive force for vertically moving the feed dog. When the sewing machine is set to its embroidery mode for sewing embroidery patterns, the solenoid is driven to retract and maintain the feed dog, via the feed dog lowering device, into a fixed retraction position.
Japanese Patent-Application Publication No. HEI-4-371189 discloses a sewing machine provided with a feed dog vertical drive mechanism including a cam body fixed to the lower shaft of the sewing machine. The cam body has two integral cams: an eccentric cam and a concentric cam. A vertical movement lever linked with the feed dog is disposed in confrontation with the cam body. During sewing of practical patterns, the vertical movement lever abuts against the eccentric cam so that rotation of the eccentric cam vertically moves the feed dog above and below the level of a needle plate. On the other hand, during sewing of embroidery patterns, the vertical movement lever is brought into confrontation with the concentric cam. Because the concentric cam has a small diameter, the vertical movement lever is lowered so that the feed dog is retracted below the needle plate into a retracted condition. Because the concentric cam is concentric, the feed dog is maintained stably in the retracted condition.
Japanese Patent-Application Publication No. SHO-61-58200 discloses a sewing machine with a movable blade that passes between the feed dog and the loop taker in order to cut a thread suspended between the feed dog and the loop taker. When the movable blade is moved to cut the thread, the feed dog is raised up to prevent the feed dog and a movement blade from interfering with each other when the thread is cut.